Field
The present subject matter relates to a facsimile apparatus, a control method thereof, and a storage medium.
Description of Related Art
In recent years, a method for performing facsimile (fax) communication using the Internet protocol (IP) network has become established. The fax communication using the IP network employs Session Initiation Protocol (SIP) as a call connection protocol, and T.38 protocol for performing data communication. Since such fax communication using the IP network is performed via the IP network, communication is performed at a higher speed as compared to a conventional G3 fax. Further, a SIP and T.38-enabled Internet fax apparatus (hereinafter referred to as an IP fax) is currently in the market.
Furthermore, a T.38 gateway (T.38 GW) which converts in real time an analog fax signal of the G3 fax into the T.38 protocol is also available in the market. The T.38 GW thus allows the SIP and T.38-enabled IP fax and the conventional G3 fax to communicate with each other.
Communication using the T.38 protocol utilizes, for the transport layer, either Transmission Control Protocol (TCP)/Transport Protocol Data Unit Packet (TPKT), or User Datagram Protocol (UDP)/UDP Transport Layer Protocol (UDPTL).
The protocols available for communication using the T.38 protocol are determined as below according to environmental specifications in which IP fax communication is to be performed.
Public IP network: TCP/TPKT, UDP/UDPTL
Local IP network A (using a predetermined exchanger): UDP/UDPTL
Local IP network B (using peer-to-peer (P2P) method): TCP/TPKT, UDP/UDPTL
T.38 GW: UDP/UDPTL
The predetermined exchanger is a local IP exchanger which includes an SIP server and resolves on the local IP network a connecting destination address based on a destination telephone number. Further, P2P is a communication method which directly connects terminals to each other on the IP network to allow the terminals to transmit and receive data using IP addresses thereof.
If the size of an internet facsimile protocol (IFP) packet is increased and the number of packets is decreased in both the TCP/TPKT and UDP/UDPTL protocols, extra data of a header portion to be transmitted to the network can be decreased. Throughput is thus improved. Further, in the case of using the UDP/UDPTL protocol, if the number of redundant packets for performing error recovery is increased, tolerance to packet loss is improved. However, if the number of redundant packets is excessively increased, the throughput is lowered, so that real-time property becomes degraded.
Thus, it is necessary to appropriately determine the packet size according to the environment in which communication using the T.38 protocol is to be performed.
Japanese Patent Application Laid-Open No. 2002-158702 discusses a method for determining the packet size for a GW apparatus and a router apparatus. More specifically, Japanese Patent Application Laid-Open No. 2002-158702 is directed to a technique for reducing, when performing real-time communication such as voice communication, a packet delay time, and at the same time improving the throughput when performing non-real-time communication such as data communication including a file transfer. Japanese Patent Application Laid-Open No. 2002-158702 thus discusses a technique for dividing and transmitting packets when performing real-time communication.
Among T.38 GWs used for performing communication between the T.38-enabled IP fax and the G3 fax, there is a GW in which restrictions are placed on a receivable packet size. More specifically, the total size of the packet is restricted to less than 320 bytes, and the size of the IFP packet is restricted to less than 128 bytes.
For this reason, there is a problem in that the packet not satisfying the above-described restrictions on the packet size becomes discarded on the T.38 GW side, so that IP fax communication cannot be normally performed. Japanese Patent Application Laid-Open No. 2002-158702 does not discuss adjusting the packet size with respect to the size restrictions on the above-described data portion.
In general, when communicating with a T.38 GW, the UDP/UDPTL protocol is available for the transport layer in the T.38 protocol. In the case of a Voice over IP gateway (VoIP GW) used for voice communication, a small amount of packet loss which occurs in VoIP is negligible, so that the UDP protocol is generally used. Since the T.38 GW is a variation of the VoIP GW, the T.38 GW also generally uses the UDP protocol.
Thus, the above-described size restrictions can be overcome by performing packetization, specifically, by reducing the size of the IFP packet of a UDPTL packet and decreasing the number of redundant packets used for error recovery. However, if the packet size is uniformly reduced regardless of the connection destination, the data amount of the header portion to be transmitted to the network relatively increases, so that the throughput is lowered in the environment other than the T.38 GW. Further, if the number of redundant packets used for error recovery becomes small, the tolerance to packet loss may also be lowered.